linux-kernel - Re: [PATCH net-next] vhost: use "checked" versions of get_user() and put

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <CACGkMEtQZ3M-sERT2P8WV=82BuXCbBHeJX+zgxx+9X7OUTqi4g@mail.gmail.com>
Date: Thu, 13 Nov 2025 09:09:55 +0800
From: Jason Wang <jasowang@...hat.com>
To: Jon Kohler <jon@...anix.com>
Cc: "Michael S. Tsirkin" <mst@...hat.com>, Eugenio Pérez <eperezma@...hat.com>, 
	kvm@...r.kernel.org, virtualization@...ts.linux.dev, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Linus Torvalds <torvalds@...ux-foundation.org>, 
	Borislav Petkov <bp@...en8.de>, Sean Christopherson <seanjc@...gle.com>
Subject: Re: [PATCH net-next] vhost: use "checked" versions of get_user() and put_user()

On Thu, Nov 13, 2025 at 8:14 AM Jon Kohler <jon@...anix.com> wrote:
>
> vhost_get_user and vhost_put_user leverage __get_user and __put_user,
> respectively, which were both added in 2016 by commit 6b1e6cc7855b
> ("vhost: new device IOTLB API").

It has been used even before this commit.

> In a heavy UDP transmit workload on a
> vhost-net backed tap device, these functions showed up as ~11.6% of
> samples in a flamegraph of the underlying vhost worker thread.
>
> Quoting Linus from [1]:
>     Anyway, every single __get_user() call I looked at looked like
>     historical garbage. [...] End result: I get the feeling that we
>     should just do a global search-and-replace of the __get_user/
>     __put_user users, replace them with plain get_user/put_user instead,
>     and then fix up any fallout (eg the coco code).
>
> Switch to plain get_user/put_user in vhost, which results in a slight
> throughput speedup. get_user now about ~8.4% of samples in flamegraph.
>
> Basic iperf3 test on a Intel 5416S CPU with Ubuntu 25.10 guest:
> TX: taskset -c 2 iperf3 -c <rx_ip> -t 60 -p 5200 -b 0 -u -i 5
> RX: taskset -c 2 iperf3 -s -p 5200 -D
> Before: 6.08 Gbits/sec
> After:  6.32 Gbits/sec

I wonder if we need to test on archs like ARM.

Thanks